1. Technical Field
Devices and apparatuses consistent with the present disclosure relate to extreme ultraviolet radiation and, more particularly, to a connection device provided between an extreme ultraviolet radiation source and an extreme ultraviolet radiation receiving device.
2. Related Art
FIG. 7 shows an example of a configuration of a related-art connection device between an extreme ultraviolet radiation source (hereinafter, referred to as an “EUV radiation source”) and a chamber containing an exposure tool. FIG. 7 is a cross-sectional view taken along an optical axis.
The EUV radiation source has a chamber 10 as a discharge vessel. The chamber 10 of the EUV radiation source includes a first chamber 10a and a second chamber 10b. The first chamber 10a is provided with a discharge portion 1 for heating and exciting an EUV radiating species. The second chamber 10b is provided with an EUV collector mirror 2 for collecting EUV radiation. The EUV radiation is emitted from high temperature plasma generated from the EUV radiating species heated and excited by the discharge portion 1.
The EUV collector mirror 2 collects the EUV radiation, and guides the EUV radiation from an EUV radiation output portion 4 of the second chamber 10b to an irradiation optical system including an exposure tool (not shown).
The first chamber 10a is connected to exhaust unit 9c. The second chamber 10b is connected to a first gas supply unit 16a and a second gas supply unit 16b for supplying cleaning gas or the like and also is connected to a first gas exhaust unit 9a and a second gas exhaust unit 9b. The insides of the chambers 10a and 10b are depressurized by the gas exhaust units 9a, 9b, and 9c. 
In the discharge portion 1, a first discharge electrode 11 as a disk-shaped member made of metal and a second discharge electrode 12 as a disk-shaped member made of metal are disposed with an insulator 13 interposed therebetween.
The center of the first discharge electrode 11 and the center of the second discharge electrode 12 are substantially on the same axis, and the first discharge electrode 11 and the second discharge electrode 12 are fixed at positions away from each other by a thickness of the insulator 13. A diameter of the second discharge electrode 12 is larger than that of the first discharge electrode 11. The thickness of the insulator 13, that is, a distance between the first discharge electrode 11 and the second discharge electrode 12 is about 1 mm to about 10 mm.
A rotating shaft 6a of a motor 6 is attached to the second discharge electrode 12 such that the center of the first discharge electrode 11 and the center of the second discharge electrode 12 are substantially on the same rotating axis of the rotating shaft 6a. The rotating shaft 6a is introduced into the chamber 10 with, for example, a mechanical seal. The mechanical seal allows the rotating shaft 6a to rotate with the depressurized atmosphere kept in the chamber 10.
A first wiper 12a and a second wiper 12b formed of, for example, carbon brush or the like are provided below the second discharge electrode 12.
The second wiper 12b is electrically connected to the second discharge electrode 12. The first wiper 12a is electrically connected to the first discharge electrode 11 through a through hole 12c penetrating the second discharge electrode 12.
Insulation breakdown does not occur between the first wiper 12a and the second discharge electrode 12. The first wiper 12a and the second wiper 12b are configured as electrical contact points keeping electrical connection while the first wiper 12a and the second wiper 12b are wiped, and are connected to a pulsed power supply 15.
The pulsed power supply 15 supplies pulsed power between the rotating first discharge electrode 11 and second discharge electrode 12 through the first wiper 12a and the second wiper 12b. 
Peripheral portions of the first discharge electrode 11 and the second discharge electrode 12, which are the disk-shaped members made of metal, are tapered to produce a pointed edge. In other words, a diameter of the first discharge electrode 11 on a side facing the second discharge electrode 12 is slightly larger than a diameter of the first discharge electrode 11 on the opposite side from the second discharge electrode 12. Similarly, a diameter of the second discharge electrode 12 on a side facing the first discharge electrode 11 is slightly larger than a diameter of the second discharge electrode 12 on the opposite side from the first discharge electrode 11. When power is applied from the pulsed power supply 15 to the first discharge electrode 11 and the second discharge electrode 12 as described later, electrical discharge occurs between the tapered edge portions of the electrodes.
When the electrical discharge occurs, temperature of the vicinity of the electrodes becomes high. Accordingly, the first discharge electrode 11 and the second discharge electrode 12 are made of high melting point metal such as tungsten, molybdenum, and tantalum. The insulator is made of, for example, silicon nitride, aluminum nitride, diamond, and the like.
Solid tin (Sn) or solid lithium (Li) as a raw material for producing high temperature plasma is supplied to the discharge portion 1. The raw material is supplied from a raw material supply unit 14 to a groove portion 12d formed around the peripheral portion of the second discharge electrode 12. That is, the raw material is supplied into the groove portion 12d of the disk-shaped member that forms the second discharge electrode 12. The motor 6 rotates in only one direction, the rotating shaft 6a is rotated by the operation of the motor 6, and the first discharge electrode 11 and the second discharge electrode 12 connected to the rotating shaft 6a are rotated in one direction. Sn or Li supplied to the groove portion 12d of the second discharge electrode 12 is moved toward the EUV radiation outgoing side in the discharge portion 1 by the rotation of the second discharge electrode 12.
The chamber 10 is provided with a laser irradiator 5 for irradiating laser onto the Sn or Li that is moved toward the EUV radiation outgoing side. The laser irradiator 5 may be formed of YAG laser, CO2 laser, or the like.
The laser from the laser irradiator 5 is irradiated onto Sn or Li which is in the groove portion of the second discharge electrode 12 moved toward the EUV radiation outgoing side through a laser collecting means and a laser transmission window portion (not shown) in the chamber 10. As described above, the diameter of the second discharge electrode 12 is larger than that of the first discharge electrode 11. Accordingly, the laser passes by the side of the first discharge electrode 11 and is irradiated onto the groove portion 12d of the second discharge electrode 12.
The EUV radiation from the discharge portion 1 is radiated as follows.
The laser is irradiated from the laser irradiator 5 onto the Sn or Li in the groove portion 12d. The Sn or Li irradiated with the laser is evaporated between the first discharge electrode 11 and the second discharge electrode 12, and a part of the Sn or Li is ionized. Under such a condition, when the pulsed power supply 15 applies pulsed power, a voltage of which is about +20 kV to about −20 kV, between the first discharge electrode 11 and the second discharge electrode 12, an electrical discharge occurs between the tapered edge portions provided at the peripheral portions of the first discharge electrode 11 and the second discharge electrode 12.
At this time, pulse-shaped high current flows at the partially ionized portion of Sn or Li evaporated between the first discharge electrode 11 and the second discharge electrode 12. A high temperature plasma P is formed, at the peripheral portion of the both electrodes, from the evaporated Sn or Li by Joule heating of the pinch effect, and EUV radiation having a wavelength of 13.5 nm radiates from the high temperature plasma P. As described above, since the pulsed power is applied between the first discharge electrode 11 and the second discharge electrode 12, the electrical discharge is a pulse discharge and the radiating EUV radiation is a pulse radiation having a pulse shape.
The EUV radiation radiated from the discharge portion 1 is collected by an oblique-incidence type EUV collector mirror 2, and is guided, via the EUV radiation output portion 4 provided in the second chamber lob, to the irradiation optical system of the exposure tool (not shown) provided in a third chamber 10c. 
The EUV collector mirror 2 includes a plurality of, for example, rotating oval bodies having different diameters or paraboloid mirrors. The rotating center axes of the mirrors are overlapped with one another so that focal positions thereof substantially coincide with one another. The mirrors are configured to satisfactorily reflect EUV radiation having an oblique incident angle of about 0 to about 25 degrees by minutely coating a reflection side of a base material having a smooth surface formed of, for example, nickel (Ni) or the like, with a metal film such as ruthenium (Ru), molybdenum (Mo), or rhodium (Rh).
A foil trap 3 is disposed between the discharge portion 1 and the EUV collector mirror 2 to prevent damage of the EUV collector mirror 2. The foil trap 3 catches debris such as metal powder generated by sputtering the first discharge electrode 11 and the second discharge electrode 12 which are in contact with the high temperature plasma, or debris caused by Sn or Li that is a radiating species, and thus allows only EUV radiation to pass. The foil trap 3 includes a plurality of plates (foil) and a ring-shaped supporter for supporting the plates. The plates are disposed in a diameter direction of a high temperature plasma generating area so as not to block the EUV radiation from the high temperature plasma.
When the foil trap 3 is provided between the discharge portion 1 and the EUV collector mirror 2, pressure between the high temperature plasma P and the foil trap 3 increases and thus collision of debris increases. The debris reduces the kinetic energy by repeated collision. Accordingly, energy of the debris is reduced when the debris collides with the EUV collector mirror 2, and thus it is possible to reduce damage to the EUV collector mirror 2.
As described above, the EUV radiation radiated from the high temperature plasma P generated in the EUV radiation source is collected by the EUV collector mirror 2, and is sent out via the EUV radiation output portion 4 of the second chamber 10b. 
The EUV radiation output portion 4 is connected to an EUV radiation output portion 7 provided in a housing of the exposure tool. That is, the EUV radiation collected from the EUV collector mirror 2 enters the exposure tool through the EUV radiation output portion 4 and the EUV radiation output portion 7.
The exposure tool has an illumination optical system for application of the incident EUV radiation. The illumination optical system forms a shape of the EUV radiation incident from the EUV radiation output portion 7, and then irradiates a mask formed with a circuit pattern.
The optical system in the exposure tool has no glass material allowing the EUV radiation to pass therethrough. Accordingly, a reflection optical system is employed instead of a transmission optical system such as a lens system, and the illumination optical system includes reflection type optical elements such as one or more reflection mirrors. The light reflected by the reflection type mask is reduced and projected onto a work (for example, a wafer coated with resist) by a projection optical system, and a reduced circuit pattern of the mask is formed on the work. Similarly to the illumination optical system, the projection optical system also employs a reflection optical system, and includes reflection type optical elements such as one or more reflection mirrors.
The EUV radiation is absorbed by air, and thus components such as an illumination optical system of an exposure tool, a mask, a projection optical system, a work, and a work stage are installed in a vacuum. These components are installed in a housing of the exposure tool. Gas existing in the housing is exhausted by a gas exhaust unit, and an inside of the housing is kept at a low pressure.
The EUV radiation receiving unit 7 provided in the housing of the exposure tool and the EUV radiation output portion 4 provided in the EUV radiation source are connected to each other through a connection device 20. The inside of the chamber (second chamber 10b) of the EUV radiation source and the inside of the housing (third chamber 10c) of the exposure tool have a structure capable of differential pumping by the gas exhaust units, respectively.
In the EUV radiation source, various kinds of gas are used such as a gas for generating a high temperature plasma for radiating the EUV radiation, a gas for reducing the debris caused by the high temperature plasma or electrode materials, and a gas for cleaning an inner wall of the chamber or the collector mirror. For example, JP-T-2006-529057 describes that cleaning of debris may be performed with halogen gas.
Meanwhile, the inside of the exposure tool connected to the EUV radiation source is kept in a high vacuum state to prevent attenuation of the EUV radiation. For this reason, it is advantageous to prevent movement of gas from the EUV radiation source to the exposure tool. For example, JP-A-2004-172626 describes a related art technique for forming a barrier using a gas lock in a lithography device in which an EUV radiation source and an exposure tool are connected each other.
As described above, in the EUV radiation source for radiating the extreme ultraviolet radiation, the various kinds of gas are used. As such, the pressure of the EUV radiation source is set to about 1 Pa.
Meanwhile, the inside of the exposure tool, which is connected to the EUV radiation source and to which the extreme ultraviolet radiation is introduced, is also kept in a high vacuum state (for example, about 10−5 Pa) to prevent attenuation of the EUV radiation. Accordingly, unnecessary gas is removed from the inside of the exposure tool by performing a degassing process.
Thus, since the inner environments in the EUV radiation source and the exposure tool are different from each other, it is advantageous to prevent movement of gas from the EUV radiation source to the exposure tool on an interface between them. For example, a halogen gas used for cleaning is likely to decrease the characteristics of the optical components or to have an influence on a movement mechanism of the optical components. Accordingly, it is advantageous to prevent halogen gas from flowing into the exposure tool.
As a general blocking method for preventing the movement of gas, a physical blocking means (e.g., a gate valve, a thin film filter) has been proposed in the related art. However, in the related art gate valve, there is a disadvantage in that a connection portion is covered with a lid. Accordingly, the related art gate valve cannot be used during an exposure operation, i.e., during the generation of EUV radiation.
On the other hand, the related art thin film filter can be used during the exposure operation by selecting a material allowing the EUV radiation to pass therethrough. However, a pressure difference between the EUV radiation source and the exposure tool may be on the order of about 105 Pa. Accordingly, there is a disadvantage in that in a case where the thin film filter has a thickness capable of withstanding the pressure difference, permeability of the EUV radiation decreases.
Accordingly, for example, as described in FIG. 7, the connection device 20 is provided in a differential pumping portion between the EUV radiation receiving portion 7 of the exposure tool and the EUV radiation output portion 4 of the second chamber 10b. In other words, the connection device 20 forms an interface between the EUV radiation source and the exposure tool. Gas is supplied from a third gas supply unit 20a to the connection device 20, and thus the movement of the gas on the interface between the EUV radiation source and the exposure tool is controlled.
That is, as shown in FIG. 8, a gas for preventing the movement of gas between the EUV radiation source and the exposure tool (hereinafter “stop gas”) is supplied from the gas supply unit 20a to the connection device 20. The stop gas is allowed to flow in both directions toward the EUV radiation source and the exposure tool, and inflow of gas such as a cleaning gas from the EUV radiation source to the exposure tool is prevented.
JP-A-2004-172626 describes a related art lithography device for coupling a first chamber and a second chamber using a gas lock. In this case, the gas of the gas lock forms a barrier separating the first chamber and the second chamber.
FIG. 9 shows an example of the gas pressure of the related art connection device 20 in case of using differential pumping and a stop gas. In FIG. 9, a horizontal axis represents a distance from a stop gas inlet in a center-axis direction (i.e., an X-axis direction in FIG. 8), and the right side in the same figure represents the EUV radiation source side. A position of 0 in the horizontal axis is a center position of the stop gas inlet (in FIG. 9, the position of 0 is shown in the scale of the horizontal axis). A vertical axis represents a pressure (Pa).
A graph A represents a pressure distribution of the stop gas supplied to a differential pumping portion, and a graph B represents a pressure distribution of a gas (e.g., cleaning gas) supplied to the EUV radiation source.
As can be seen from FIG. 9, the gas on the EUV radiation source side does not flow into the exposure tool side by the operations of the differential pumping and the stop gas.
However, while the related art connection device acts to prevent gas from flowing between the first chamber and the second chamber, the related art connection device has a few disadvantages. For example, when the stop gas is supplied to the differential pumping portion as described above, a high pressure layer is formed by the stop gas with respect to a passing direction of the EUV radiation. Accordingly, there is a disadvantage in that the EUV radiation does not easily pass through the high pressure layer (i.e., a permeability decreases). For example, as shown in FIG. 9, a thickness of a part where the pressure of the stop gas is 100 Pa with respect to the passing direction of the EUV radiation is about 9 mm. To reduce the thickness of the layer, it is conceivable to reduce a supply rate of the stop gas. However, if the supply rate of the stop gas is reduced to reduce the thickness, there is a disadvantage in that gas easily flows from the EUV radiation source into the exposure tool.
As described above, in order to prevent the movement of gas, it is conceivable to use the related art gate valve or the related art thin film filter. However, the related art gate valve has a disadvantage in that the gate valve cannot be used during the EUV radiation generation. The related art film filter has a disadvantage in that the permeability of the EUV radiation decreases.